power for operation. All components of the system were off-the-shelf 

 items. On a typical backpack harness was mounted a 17x8xl/4-inch alumi- 

 num plate to which a Binks Oil-Less Air Compressor Model 34-1051 was 

 attached. This compressor, powered by a 3/4-hp, 1,725-rpm electric 

 motor, produced a maximum pressure of 50 psi. Surface preparation tools 

 included a Chicago Monarch Model 25 chipping hammer/needle gun (Figures 

 1(b) and (c)) and a Black and Decker 16,000-rpm, air-operated disc 

 sander (Figure 1(d)). The paint gun was a Binks Model 62 with a Binks 

 Model 80 1-quart pot (Figure 1(e)). Six-foot long feedlines extended 

 from the compressor to the pot and from the pot to the gun. The complete 

 system weighed approximately 67 pounds. In the field, tower electrical 

 outlets or extension cords to other outlets were to provide power for 

 operation. 



Results 



The backpack surface preparation and paint application equipment 

 was satisfactorily used in the laboratory to clean and coat the experi- 

 mental panels. When the equipment was used for surface preparation and 

 coating application on the antenna towers at PMTC, however, the following 

 problems were noted: (1) the system was too heavy to use for an extended 

 period of time; (2) electric power was not available so air pressure had 

 to be obtained from a portable compressor; and (3) the compressor pro- 

 duced inadequate pressure for satisfactory cleaning with the tools. A 

 larger portable compressor had to be used to provide the necessary 

 pressure. 



If such alternative equipment were chosen for future use, a diesel- 

 driven air compressor could be used for both cleaning and application. 

 A clamped, rigid line could run from the compressor at the base to the 

 top of the antenna. Quick disconnects for attachment of a flexible 

 pneumatic hose could be located at intervals of 20 feet. This hose 

 could be fitted to a reel mounted on the backpack harness in place of 

 the compressor and motor. While such an alternative system was not 

 tested on the vortex towers, it is believed that all problems encoun- 

 tered with the original backpack system would be eliminated by use of 

 such an system. For instance, a pressure hose was lifted in similar 

 fashion with a cherry picker. 



FIELD EXPOSURE OF COATINGS ON VORTEX TOWERS AT PMTC 



Preparation of Test Areas 



Portions of two steel vortex towers located on a beach at the 

 western perimeter of PMTC were used as substrates for the second field 

 exposure of antenna coating repair. These towers were erected in 1954 

 and have been painted three times since then. The towers are exposed to 

 periodic wind-blown sand and salt spray from the ocean, with the lower 

 20 feet subject to sand abrasion at times of high wind. Large areas of 

 the legs and chord braces had extensive coating loss and rusting. Most 

 connectors had significant galvanic corrosion. 





